A film known from U.S. Pat. No. 3,741,253 to Brax et al comprises a core layer of a vinylidene chloride copolymer (saran) between a layer of ethylene-vinyl acetate copolymer and layer of cross-linked ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymer (EVA) has some improved properties over the previously used polyethylene. Vinylidene chloride copolymers are known barrier materials to fluids such as oxygen.
As disclosed in U.S. Pat. No. 4,064,296 to Bornstein et al the core layer may also be a hydrolyzed ethylene-vinyl acetate copolymer (EVOH). It has similar oxygen barrier properties as vinylidene chloride copolymers and offers the advantage that it may be irradiated without discoloration, which is further discussed below.
Blends of linear low density polyethylene and ethylene-vinyl acetate copolymer in oriented barrier films are disclosed in U.S. Pat. No. 4,457,960 to Newsome, which claims an oriented multiple layer polymeric film, comprising (a) a first barrier layer, said first layer having two opposing surfaces; (b) a second layer adhered to one said surface, said second layer being 10% to 90% linear low density polyethylene and 90% to 10% ethylene vinyl acetate; and (c) a third layer adhered to the other said surface, the composition of said third layer being selected from the group consisting of (i) ethylene-vinyl acetate, and (ii) blends of 10% to 90% linear low density polyethylene with 90% to 10% ethylene-vinyl acetate.
U.S. Pat. No. 4,640,856 to Ferguson et al, commonly assigned to W. R. Grace & Co., discloses a multi-layer, thermoplastic barrier film having at least three layers comprising: (a) a layer consisting essentially of very low density polyethylene having a density of less than 0.910 gms/cc; (b) a barrier layer comprising a material selected from the group consisting of: (1) copolymers of vinylidene chloride and (2) hydrolyzed ethylene-vinyl acetate copolymers; (c) a thermoplastic polymeric layer, said layer being on the side of the barrier layer opposite to that of layer (a); and (d) the shrinkage of layer (a) controlling the shrinkage of the entire multi-layer barrier film, said multi-layer film having been oriented and rendered heat shrinkable at a temperature below 100.degree. C. (212.degree. F.), said orientation temperature being about 40.degree. F. or more below the melt temperature of said very low density polyethylene.
"LLDPE Properties Tied to Branch Distribution", Plastics Engineering, January 1987, by Larry D. Cady of Dow Chemical Company, Freeport, Texas discusses four linear low density polyethylenes (LLDPE). Two have the same density of 0.922, the same melt index of 1.0 to 1.1, the same I.sub.10 /I.sub.2 ratio of 7.5 to 7.6, and the same octene comonomer, yet the LLDPE with an elution temperature around 85.degree. C., (FIG. 3) exhibited a higher dart impact of 330 g (Table) than the LLDPE with an elution temperature around 100.degree. C. (FIG. 3) which exhibited a lower dart impact of 193 g (Table).
It is an object of this invention to provide a packaging film and bags made therefrom having excellent abuse resistance and thereby provide a minimal risk of breakages when bags made of the film material are utilized in automated loading processes. The main use of the bags is in packaging large cuts of meat, which often have bony projections and large cavities.
It is another object of this invention to provide a heat-shrinkable material for films and bags having the above advantage yet retaining good shrinkability characteristics, and good orientation processing characteristics.